The invention relates to a diaphragm pump, designed as a hydraulically activated reciprocating pump, especially for the pumping of a viscous and abrasive medium or for one which is a secondary flowable medium charged with solid materials, and having a pump section through which the secondary medium flows. The pump section is insertable as an integrated part of a pipe line for the secondary medium to be delivered, and has a return valve at the suction as well as the pressure side. An operational portion designed as a separate unit is coupled with the pump section by means of a connecting fitting carrying a primary flowable operational medium. The primary operational medium affecting the inside of a tubular membrane is made of elastomer material, having the shape of a cylindrical hose. The pump operates the membrane by means of pulsating pressure, while the secondary medium is located in the pump chamber surrounding the membrane.
Diaphragm pumps of the initially described type are known from U.S. Pat. Nos. 1,832,259 and 2,092,629, in which the diaphragms in the shape of a cylindrical hose are tensioned into essentially cylindrical housings with their respective ends. These diaphragm pumps, because of their specific geometric relations between a tube membrane and a cylindrical housing, are not suited for the delivery of media carrying more or less granular solid matter, since the latter, not being able to divert, are driven into the surface of the hose, especially within the relatively narrow pump chamber, within the area of the tensioned clamping of the tubular membrane.
Thus, the disclosed state of the art indicates that, while the mode of operation of the known diaphragm pumps in principle corresponds to that of the initially described type, the constructive design of the pumps of record does not permit the delivery of heavy, viscous and abrasive fluids as well as of fluids charged with solid matter.
Austrian Pat. No. 288 870 describes a hose pump for dense viscous matter, for concrete or bulk materials in which the operating medium and the material to be delivered are separated by an elastic hose, the liquid or gaseous operating medium being within said hose, and the material to be delivered being between said hose and the surrounding pump housing, within thus formed annular space. This hose pump which has no valves is characterized by being sub-divided into at least three subsequently arranged chambers in which elastic tubes are arranged by means of concentric inner bodies, the hoses at their ends being fastened and sealed to the said inner bodies, their middle parts being pressed against the chamber walls by way of chamber connections and the introduction of operating media flowing within the inner bodies, and which, being relieved of pressure and contracting by their own elasticity, come to rest against the inner body once more. In this hose pump of record, each of the hose membranes temporarily performs the functions of the lacking return valves, cooperating with the surrounding cylindrical housing wall. Should a pump of this type be used for the delivery of media containing coarse solid matter, the danger arises during the phase where the hose membrane is pressed against the surrounding cylindrical housing wall, that individual solid particles, unable to be diverted, will be driven into the hose surface and will destroy it in due time.
Another solution of the task with regard to the medium to be delivered as well as from the viewpoint of sufficient longevity is achieved by another diaphragm pump, characterized by the use of a sheet diaphragm in place of a tubular elastomer membrane. The known standard designs hardly present problems regarding the delivery of media which are charged with solid matter, nor are there any problems with longevity, inasmuch as sheet diaphragms are merely vaulted and thus come under tensile stress. Lately, the need for, and the application of, diaghragm pumps, especially in the area of environmental protection, has been increased, requiring these pumps to handle densely viscous and abrasive media or such media which are charged with solid materials. At the same time, these pumps are required to be not only more efficient but also more economical than the past designs. The requirements of higher efficiency require for all known designs an increase in the dimensions of the diaphragm housing. It is true that diaphragm pumps with sheet membranes may be increased in size without any problems. This, however, results in considerable wall thicknesses for these usually short, cylindrical pump housings with large diameters, in particular in the area of the circular covers. Thus, for instance, the cover wall thickness of a gray cast iron housing with a diameter of 500-600 mm, is 20 mm and more. Given these dimensions, the demands for a diaphragm pump which is equally efficient as it is economical can no longer be met.
Basic considerations have shown that the demands of the market for a well-priced diaphragm pump with high efficiency and high delivery pressure may be met with the aid of pumps of the initially described type if it is possible to design this type of pump in such a manner that densely viscous and abrasive, as well as media abrasive loaded with solid materials, may be delivered. It was the finding of the aforementioned considerations dealing with pump behaviour that, given approximately identical outer dimensions for the pump housing, hose membrane pumps, with a hose membrane affected by the operating medium from the inner side, deliver about double the suction volume than the diaphragm pump with a sheet membrane, having assumed a condition that the required membrane displacements during the pressure lift would be about identical. The kinematic reversal of a pump design, deemed especially advantageous, and leading to a pump in which the hose membrane is compressed from the outside by the operating medium, is not suitable because, first, the elastomer materials in use at the present time are susceptible to strain and, second, maximum efficiency of delivery can be obtained only with an inflated, distended hose and not with one which is compressed.
It is the purpose of the present invention to design the diaphragm pump of the initially described type in such a manner that the greatest possible suction volumes or delivery flows and delivery pressures, respectively, can be obtained coupled with a lowest possible weight or, respectively, the smallest possible dimensions. In doing so, the extension of the hose membrane required for the realization of a given lift volume is to be reduced to the lowest possible value. The requirement of maximum efficiency with a minimum of constructive expenditure should, in addition, apply also to all other peripheral units of the pump aggregate, resulting in a minimizing of costs.
This purpose is achieved by surrounding the pump chamber by an outer, preferably spherical housing and the outer surface of the hose membrane which, with its both ends is stretched and clamped within the housing.
The design of the pump chamber according to the invention makes it possible to fabricate the housing, which, ideally, should be ball-shaped, as a steel plate construction. It is a known fact that spherical housings provide the greatest possible stability with the lowest possible material consumption. In addition, the spherical housing permits the use of a hose membrane with a large diameter which results in the greatest possible lift volume. The clamping of the membrane at its both sides within the spherical housing furthermore is of great advantage, inasmuch as the spherical housing may be opened by lifting a cover without the hose membrane having to be dismantled at the same time. The spherical housing in addition makes sure that at the point of the greatest distension of the membrane, the greatest clearance of the spherical housing is available. This prevents an attachment of the hose membrane to the wall of the spherical housing while, at the same time, achieving the advantage that the suction as well as the pressure muff arranged in this area are freely accessible to the medium to be delivered. In order to prevent a membrane rupture and, as a consequence, damage to the operating part especially by abrasive media, two cylindrical hose membranes are provided, the outer membrane concentrically sheathing the inner one without interstices. This arrangement of two hose membranes sheathing each other is known from the aforementioned U.S. patents, where, however, they are arranged in essentially cylindrical housings.
Additional basic considerations as were referred to above, gave the result that, given approximately identical outer dimensions for the pump housing, the hose membrane pump gave about double the volumetric suction yield of a comparable diaphragm pump with a sheet membrane. These excellent results regarding the suction volume are countered by an essentially greater maximum surface extension of the material of the hose membrane. Thus, for instance, a hose membrane giving the double volume lift of a sheet membrane, will be stretched three times as much in the area of its maximum distension than the sheet membrane in the area of its respective greatest stress. The surface extension of the aforementioned hose membrane still remains about double that of the surface extension of the sheet membrane even if the excursion of the hose membrane is reduced to a point where the lift volume is only half, i.e. where it is adapted to the lift volume of the unchanged excursion of the sheet membrane. These grave differences can be proven mathematically. As can be easily determined, the circumferential extension of the hose membrane is in direct proportion to its radial excursion, while the corresponding arching of the sheet membrane, from a mathematical viewpoint, does not react as strongly to the relations for the uniaxial stretching of the arched sheet membrane. Supporting papers indicate that it is not the occurring surface stretch which would influence any judgement of tolerable stretches of a membrane material, but the longitudinal, linear stretch deduced as an equivalent. This equivalent linear stretch is approximately twice as great as the actually occurring surface stretch and is utilized as a dimensioning criterion when deciding on the size of the membrane. While it is true that modern membrane materials, the so-called elastomer vulcanized materials, are substantially resistant to breakage in extension, these values cannot be utilized when dimensioning the membrane. In practical use, linear distensions of more than 25% should possibly be avoided since, with an increased extension, the danger of permanent deformation cannot be excluded. As a rule, this value is reached nearly all the time by sheet membranes, while hose membranes in pumps according to the invention nearly always exceed it considerably in nearly every comparable application. The manufacturers of membrane material are not yet in a position of giving quantitative information regarding the residual extension of the possible materials, given the aforementioned considerable linear extensions, but experience has shown that the resulting permanent stretch cannot be neglected. As an example, this may have as a consequence that, after a certain load alternation, the permanently stretched hose membrane, following the pressure lift, no longer rests against the support pipe over its entire surface, because of its elastic contraction but that it is subject to life-shortening stress and is pressed against the support pipe during the suction lift while forming folds and creases.